All of the sets in the GX-600 line are 10.5" reel capable, but, then there
is also the GX-400D. One thing that all the GX-6xx sets have in common, prior
to the GX-635D, is that the Pinch Roller is located above the Capstan, and it
moves down to engage. I'm not real sure how the GX-400 differs from sets like
the GX-600, and GX-650D, it too is a 10.5" reel machine, and its Pinch Roller
is above the Capstan. Note the GX-400's really large VU Meters, and the Dual
Capstans present on the GX-400D ( like in the GX-650D, it has Belt Driven
Capstans ). But well, based on their pictures, massive sets both are, they
are definately early vintage GX sets, probably from around 1972, but still...
a bit of a mystery:
Perhaps the earliest units in the 600 Series were the GX-600D and
GX-600DB. I suspect these two and the GX-650D are somewhat similar designs,
and similar vintage, despite many other sets being numerically numbered
Here are two pictures of the GX-600DB, which, of course, is the version
of the GX-600 with built-in Dolby B circuit boards, one with the rear cover
off, allowing you to see the capstan motor belt attached to the massive
Capstan flywheel, as well as all the plug-in circuit boards in the lower half.
Off on the center right is the power transformer. The layout of this set
is a bit unusual, most Akai decks have the power transformer up at the top,
near the cooling slots. I wonder if this led to more power transformer
failures than normal ?
Here is a picture of a late 1970's vintage GX Series unit the GX-620D
chronologically, I believe the GX-620 ( and the GX-625, GX-636, GX-646 )
are much later sets than the GX-400D, GX-600D, or the GX-630D. The much
later GX-620D looks like a slightly overgrown GX-255, and these two sets
incorporate the lighted when operating smoked grey function buttons, the
IC logic control circuitry, and many of their internal parts are indeed
the same. Some later versions of the GX-620D also have a front panel
pitch control, but that later version set is seldom seen.
The GX-625 has a digital readout for the tape counter, and a lot of added
circuitry is dedicated to that, much of an additional 11 x 17" page schematic,
is needed to detail it, as it is pretty complicated. Another complicated
and annoying difference from other Akai sets, is the GX-625's Brake System.
It is weird, using a Digitally Controlled Detector PC Board, along with a
Brake Control PC Board; which controls a Thyristor PC Board, which is tied
directly to the 24-XO-TD Reel Motors, for electronic brake control. This is
necessary for Auto Play and Memory Play/Stop functions. When rewinding with
the memory function "on" the rewinding speed starts to slow down at counter
"0020"; where the Thyristor circuit probably starts top lower the rewind
speed, possibly by some reverse current or a shorter duty cycle. Near "0000"
the rewinding-speed is almost zero, and then finally the mechanic brakes
are engaged and the tape stops at "0000" exactly. When the auto-functions
are "off" the machine just uses the solonoid/mechanical brake bands as found
in 98% of Akai RTR sets. I suspect the complcated circuits seen here would
be more prone to additional failure-modes over time, when compared to the
simple friction/brake pad style system found on most other home-type consumer
tape decks, like the GX-630D. Well, you never know.
The last puzzle on the GX-625 is the 12 Volt Input socket on its rear.
Someone had suggested that this means the GX-625 can be DC powered on 12
Volts (as in a car). Well, I don't think so, the set would pull about 12.5
Amperes at 12 Volts to do that, and this connector looks to be one whose
capacity is under one ampere. There is also a 1 Ampere diode in series with
that jack, so whatever it is, for, it is likely for up to half an Amp or
less, and not for powering the GX-625. I had suspected that jack could be
used for powering the optional RC-70 Wireless Remote Control System, which
apparently needs a power source for the IR Receiver, and is rarely, if ever
seen. But, no, it seems it is even more simple than that, the 12 Volt DC
Jack is simply to maintain the Counter Number in memory when the machine is
powered off. And they didn't think of using a battery for that... Otherwise,
the GX-625 is much like the GX-620.
Here is a picture of a late 1970's vintage GX Series unit the GX-625:
Here is a picture of a late 1970's vintage GX Series unit the GX-630D:
Here is a picture of a late 1970's vintage GX Series unit the GX-630DB which
has a set of simultaneous Encode / Decode Dolby B boards inside:
Here is a picture of an early 1980's > vintage GX Series unit
Chronologically, the GX-636 and GX-646 came after the GX-635D, but are
very similar sets. The later versions were EE Tape Capable, but have few
significant other differences.
Here is a picture of an early 1980's > vintage GX Series unit the GX-636:
Here is a picture of an early 1980's > vintage GX Series unit the GX-646:
And here is are two pictures of the GX-646 in Black:
Here is a picture of an early 1970's > vintage GX Series unit the
GX-650D, which is a very interesting, and unique set. Despite the higher
numerical moidel number, it is actually one of the earlier Series 600 sets.
It was perhaps the first to incorporate the Akai Servo-Controlled Capstan
Motor. It features three speeds, and I believe it was the only set in the
GX Series to do so. Now about that Servo Control... it used a huge external
servo-sensing "head" which happened to look quite a bit like one of the
prior generation pre-GX permalloy playback heads. Hey, maybe Akai had
thousands of those parts left over, and when they needed something
to do with them... instead of making another "older style" set, they
designed the new servo-controlled motor system and re-used the older
heads as the servo-feedback pickup...
In addition, what might seem like an over design, or an oxymoron...
Akai also used a belt drive from the Servo-Controlled Motor Rotor to
power the dual capstans. While this should result in very good wow
and flutter, at least in theory, it does mean a lot of extra precision
parts and components. These extra parts and components causing many
additional and varied eigenodes of flutter components, at various
frequencies and spectrum. So did Akai improve things, or make it
worse with this Servo-motor and belt drive / dual capstan design ?
That is very, very difficult to tell, without doing months of precise
measurements, but suffice it to say, all of the later Akai Series 600
sets ( GX-630D, GX-635D, GX-636, GX-646, GX-747, etc. ) used a single
capstan, and a direct drive servo-motor - where the motor rotor is
the capstan shaft. I wonder how many people were on that GX-650D
design team ??? Still, the GX-650D is an interesting older GX Series
set, on its own terms.
Here is a picture of one of the last GX Series units, perhaps the
most expensive high-end home type or consumer decks, the GX-747, which
used a bargraph of red leds, while the GX-747dbx, which incorporated
early DBX 2:1 Type I compression / expansion, used normal VU meters
in place of the led display:
Perhaps the last home consumer deck from Akai, the GX Series unit, the
Here are some pictures of the late 1980's GX-77, which, was
perhaps the most unorthedox, and unusual, Akai designed R-R Deck.
Departing from the other 10.5" capable sets on this page, it was
made in a 7" reel capable deck only. It was unusual for its
mirrored head design, two sets of three heads, which face each
other and the tape was brought up to them. It had two capstans,
but only one was used in each direction ??? The tape, in effect,
is threaded and then pulled up, in between the sets of heads much
more or less, like what is done inside a VCR, when the tape is
pulled from the cassette.
Also unusual, is that this model used small 12 Volt DC motors for
the FF and REW motors and some fancy transistor circuitry for
the braking. I suspect the motors are a bit wimpy for the task,
which appears to have been partially responsible for the sets'
reduced power consumption. Despite the advanced features and motor
electronics, it also used two internal rubber belts to drive the
reel hubs. Exotic electronics, fancy DC motors, and then a retro
step backwards ??? I suspect the GX-77 is more prone to jamming
and similar loading problems; as well as problems resulting from
tape shed and oxide clogging of the tape path. Possibly more so
than any of the more conventional three motor Akai's.
I also suspect that in the event of a motor reel hub being "held back"
in "Rewind" or "Fast Forward" the design using the belt drive is
to prevent the motor from held being motionless, in its high
voltage mode, thus eventually burning out all that sophisticated
electronics associated with it.... just a guess. But despite its
potential for being more problematic, the GX-77 is a very popular
Akai unit, with a high resale value, most probably due to its very
unusual "look" ( like a big cassette deck ) advanced design ( it
is EE Tape Capable ), and the high end features; including the
peak reading led bargraphs, and perhaps, that no comparable 10.5"
reel version exists: